From a631d27b53ccb4da2c4fcca86087053a5a518e46 Mon Sep 17 00:00:00 2001
From: Sam Martin <sam.martin@wolt.com>
Date: Sat, 23 May 2026 17:07:41 +0200
Subject: [PATCH 1/2] Add HTTP/2 machine timeout message cleanup regression
 test

---
 src/cow_http2_machine.erl | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/cow_http2_machine.erl b/src/cow_http2_machine.erl
index 26350b0..609a249 100644
--- a/src/cow_http2_machine.erl
+++ b/src/cow_http2_machine.erl
@@ -270,6 +270,31 @@ terminate(#http2_machine{preface_timer=PTRef, settings_timer=STRef}) ->
 		_ -> erlang:cancel_timer(STRef, [{async, true}, {info, false}])
 	end.
 
+-ifdef(TEST).
+
+terminate_removes_stray_timeout_messages_test() ->
+	PTRef = erlang:start_timer(5000, self(), {?MODULE, undefined, preface_timeout}),
+	STRef = erlang:start_timer(5000, self(), {?MODULE, undefined, settings_timeout}),
+	PTMsg = {timeout, PTRef, {?MODULE, undefined, preface_timeout}},
+	STMsg = {timeout, STRef, {?MODULE, undefined, settings_timeout}},
+	self() ! PTMsg,
+	self() ! STMsg,
+	terminate(#http2_machine{preface_timer=PTRef, settings_timer=STRef}),
+	[] = collect_timeout_messages(PTRef, STRef),
+	ok.
+
+collect_timeout_messages(PTRef, STRef) ->
+	receive
+		{timeout, PTRef, {?MODULE, undefined, preface_timeout}} ->
+			[preface_timeout|collect_timeout_messages(PTRef, STRef)];
+		{timeout, STRef, {?MODULE, undefined, settings_timeout}} ->
+			[settings_timeout|collect_timeout_messages(PTRef, STRef)]
+	after 0 ->
+		[]
+	end.
+
+-endif.
+
 -spec init_stream(binary(), State)
 	-> {ok, cow_http2:streamid(), State} when State::http2_machine().
 init_stream(Method, State=#http2_machine{mode=client, local_streamid=LocalStreamID,

From b527a73d8a9e2d209588e6d45e96b2ba73c8fc9d Mon Sep 17 00:00:00 2001
From: Sam Martin <sam.martin@wolt.com>
Date: Sat, 23 May 2026 17:08:04 +0200
Subject: [PATCH 2/2] Remove stray HTTP/2 machine timeout messages on terminate

---
 src/cow_http2_machine.erl | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/cow_http2_machine.erl b/src/cow_http2_machine.erl
index 609a249..0ca9c2e 100644
--- a/src/cow_http2_machine.erl
+++ b/src/cow_http2_machine.erl
@@ -261,13 +261,22 @@ setting_from_opt(Settings, Opts, OptName, SettingName, Default) ->
 
 -spec terminate(State::http2_machine()) -> ok.
 terminate(#http2_machine{preface_timer=PTRef, settings_timer=STRef}) ->
-	_ = case PTRef of
-		undefined -> ok;
-		_ -> erlang:cancel_timer(PTRef, [{async, true}, {info, false}])
-	end,
-	_ = case STRef of
-		undefined -> ok;
-		_ -> erlang:cancel_timer(STRef, [{async, true}, {info, false}])
+	cancel_timeout(PTRef),
+	cancel_timeout(STRef).
+
+cancel_timeout(TRef) ->
+	ok = case TRef of
+		undefined ->
+			ok;
+		_ ->
+			%% Do a synchronous cancel and remove the message if any
+			%% to avoid receiving stray messages.
+			_ = erlang:cancel_timer(TRef, [{async, false}, {info, false}]),
+			receive
+				{timeout, TRef, _} -> ok
+			after 0 ->
+				ok
+			end
 	end.
 
 -ifdef(TEST).